Numerical Simulation Of Laboratory Leakage Lests And Establishment Of Infiltration Models Based On HYDRUS

Under the increasingly scarce water resources environment,the effective and rational use of agricultural water resources to improve the efficiency of irrigation water use in China has become a very important issue.In order to improve the efficiency of irrigation water use,provide scientific and reasonable technical support for the design of irrigation channels,an indoor simulation experiment of channel leakage was conducted based on the studies of domestic and foreign scholars in recent years.Based on the measured data and simulated data,the influencing factors of the infiltration process were analyzed,and a cumulative infiltration capacity and wetland transport distance calculation model that can describe the test process was established.Based on the measured and simulated data,the influencing factors of the infiltration process were analyzed,and established calculation models that can describe cumulative infiltration and wetting front migration distance during the test process.The main contents and conclusions are as follows:(1)In order to analyze the rules of channel infiltration,laboratory leakage simulation tests were conducted under different channel widths,infiltration heads,slope coefficients,soil bulk density and soil initial moisture content.The experiment was conducted twice in total and carried out 26 times.The experimental equipment consisted of a cuboid soil device and a water supply system.The cuboid soil device was made from 10-mm-thick plexiglass material.The device was60 cm long,20 cm wide and 110 cm high.The rear side of the soil device was affixed with a scale bar that could directly collect data.The Mariotte flask with a flexible hose was connected to a10-mm-diameter rubber hole on the device surface to supply water.The diameter of Mariotte flask was 20 cm,and the height was 80 cm.According to the international soil classification standard,the test soil samples belong to sandy loam.The physical parameters of soil samples with different bulk density were measured.The soil saturated moisture contents with the bulk density of 1.3g/cm~3,1.35g/cm~3 and 1.4g/cm~3 were 48.1%,43.8%and 41.6%,the saturated hydraulic conductivity of the soil was 0.0936 cm/min,0.0736 cm/min,and 0.0485 cm/min,respectively.The soil water characteristic curves of different bulk density soils were tested,and the water-suction force S and volumetric moisture content?were obtained as a power function distribution.With the increase of soil bulk density,the corresponding soil water suction was slightly increased.(2)In order to solve the process of soil moisture movement under test conditions,a two-dimensional unsaturated soil moisture equation was established.The computer software HYDRUS-2D based on finite element was used to solve the equation.To solve the above partial differential equations,the horizontal and vertical distances of wetting front migration and cumulative infiltration under the experimental design procedure were simulated using HYDRUS-2D software.The simulation results and the measured results were compared and analyzed,and the mean absolute error(MAE)and root mean square error(RMSE)of the simulated and measured values were calculated.As indicated by the results,the average value of MAE for cumulative infiltration in the first laboratory test was 1329 ml,the average value of RMSE was1555 ml,and the second time was 570 ml,641 ml,respectively;The average value of MAE for horizontal distance in the first laboratory test was 1.37 cm,the average value of RMSE was 1.52cm,and the second time was 0.96 cm,1.08 cm,respectively;The average value of MAE for vertical distance in the first laboratory test was 1.46 cm,the average value of RMSE was 1.66 cm,and the second time was 1.23cm,1.44 cm,respectively.It shows that the established equation of soil water movement is reasonable,the choice of parameters is appropriate,and the soil moisture movement process under different experimental settings can be simulated.(3)The effect of channel base width on the infiltration process is extremely significant.With the increase of the base width of the channel,the cumulative infiltration volume and the wetting front migration distance increase significantly.The cumulative infiltration and the wetting front migration distance were positively correlated with the infiltration head,and the infiltration head has a significant effect on the horizontal distance.Slope coefficient has little effect on the infiltration process.With the increase of initial soil water content,the cumulative infiltration volume decreased,and the distance of wetting front migration increased.The horizontal distance increased significantly.The influence of soil bulk density on the infiltration process is mainly reflected in the decrease of cumulative infiltration and wetting front migration distance as the soil bulk density increases,and the influence of soil bulk density on vertical distance is the most significant.The results of two-factor variance analysis showed that there was no significant interaction between the factors.When designing irrigation channels,appropriate increase in channel width and infiltration head is more conducive to the growth of shallow root crops.If the water content in the field is low,irrigation should be done in time to increase the speed of water reaching the roots of plants and improve the efficiency of irrigation water use.Deep-rooted crops can be planted on looser soil channels as required.(4)In order to describe the soil moisture infiltration process under test conditions more properly,models of cumulative infiltration and wetting front migration distance considering the channel base width,the infiltration head,the slope coefficient,the initial water content and the soil bulk density were proposed based on the measured data of the second simulation test.To simplify the model,the standard regression coefficient of the soil bulk density,the initial water content,the channel bottom width,the infiltration water head,and the slope coefficient were calculated.The effects of five factors on the parameters were analyzed.Finally,the effects of the slope coefficient were eliminated,and the infiltration model was built considering the channel base width,the infiltration head,the initial moisture content,and the soil bulk density.To verify the accuracy of the simplified model,HYDRUS-2D software was used to simulate 8 groups of laboratory experiments for different soil bulk density,initial water content,channel base width and infiltration head conditions.The average MAE and RMSE values for the simulated and calculated results of cumulative infiltration,the horizontal and vertical distance of wetting front migration were-743 ml,867 ml,and-0.06 cm and 1.11 cm,1.13 cm,and 1.50 cm,respectively.These results indicate that the simplified model can effectively describe cumulative infiltration and wetting front migration under the simulated test conditions and that the model is reliable.In conclusion,analyzing the influencing factors of channel leakage and the establishment of cumulative infiltration and wetting front migration distance calculation models considering each influencing factor can provide a reference for the rational design of irrigation channels and reduce the loss of water caused by channel leakage.It will help improve the efficiency of farmland irrigation water use and ease the current low efficiency of irrigation water use.It has important reference significance for the rational use of agricultural water resources in China.